The present invention relates to an apparatus for producing a grid for a battery plate by using a rotary expander, and a method of producing such a grid.
A battery plate of a lead storage battery is configured by filling an active material into meshes of a grid made of lead or a lead alloy. Such a grid is often produced by directly forming a grid-like shape by means of, for example, casting of lead or a lead alloy, or alternatively by forming meshes in a lead sheet made of lead or a lead alloy by an expander. Expanders for this purpose include an expander of the reciprocal type in which meshes are sequentially formed in a lead sheet with starting from both the ends of the sheet, by vertical motions of a die cutter, and that of the rotary type in which slits are formed in a lead sheet in a zigzag pattern by rotation of disk cutters (a slit forming step), and the lead sheet is stretched from both the sides to expand the slits into meshes (an expanding step).
FIG. 3 shows a configuration example of a conventional production apparatus in a slit forming step in an expander of the rotary type (rotary expander). In the rotary expander, on the right side of one disk cutter roll 1 in the figure, another disk cutter roll 2 is placed, and a further disk cutter roll 3 is placed below the disk cutter roll 2 in the figure. A lead sheet 4 made of lead or a lead alloy is passed between the three disk cutter rolls 1 to 3. In each of the disk cutter rolls 1 to 3, a large number of disk cutters 5 are arranged and fixed on a common rotation shaft with being separated from each other by a distance which is approximately equal to the thickness of one disk cutter 5.
Each of the disk cutters 5 is configured by a metal disk. As shown in FIG. 4, ridges 5a in which the peripheral side face protrudes in a ridge-like shape toward the outer periphery from a reference circumferential face of a predetermined radius centered at the axis of the disk, and valleys 5b in which the peripheral side face composed of a face substantially extending along the reference circumferential face is formed are alternately formed in a whole periphery in the circumferential direction. Although not so shown in FIG. 4, the disk cutters 5 of the disk cutter rolls 2 and 3 excluding the disk cutter roll 1 are configured in the following manner. In each of the valleys 5b, a groove 5c which is opened in the peripheral side face of the valley 5b is formed in a radial direction so that the grooves which are formed in every pair of valleys 5b adjacent to each other via the respective ridge 5a are arranged so as to be alternate on peripheral edges of both the disk faces. In FIGS. 4(b) and 4(c), the peripheral edge of one disk cutter 5 is shown in a partially enlarged manner while linearly developing the circumference.
The three disk cutter rolls 1 to 3 in each of which the thus configured disk cutters 5 are arranged are placed so that the axes of the rolls horizontally elongate in parallel to one another and the ridges 5a of the disk cutters 5 alternately engage each other. Specifically, in each of the disk cutters 5 of the left disk cutter roll 1, each ridge 5a which reaches the right end enters between the ridges 5a in the left end of the corresponding disk cutters of the right disk cutter roll 2, and, in each of the disk cutters 5 of the right disk cutter roll 2, each ridge 5a which reaches the lower end enters between the ridges 5a in the upper end of the corresponding disk cutters 5 of the lower disk cutter roll 3. The disk cutters 5 of the right and lower disk cutter roll 2 and 3 are placed so that the valleys 5b of the disk cutters slightly overlap with each other.
When the lead sheet 4 is passed between the left and right disk cutter rolls 1 and 2, the ridges 5a of the disk cutters 5 overlap with each other to cut the lead sheet 4, whereby a large number of slits 4a are formed as shown in a plan view in the circle C1 of the one-dot chain line of FIG. 3. The portions between the slits 4a which are arranged in the width direction of the lead sheet 4 are pressed by the ridges 5a of the disk cutters 5 to alternately protrude to both sides in a ridge-like shape from the faces of the lead sheet 4, and formed as wires 4b. When the lead sheet 4 is passed between the upper and lower disk cutter rolls 2 and 3, the edges of the disk cutters 5 on the side where the grooves 5c of the valleys 5b are not formed vertically overlap with each other to cut the lead sheet 4, and the slits 4a which are arranged in the advancing direction of the lead sheet 4 are connected to each other as shown in a plan view in the circle C2 of the one-dot chain line of FIG. 3. The portions where the slits 4a which are arranged in the advancing direction of the lead sheet 4 are not connected to each other are formed as nodes 4c. Therefore, the slits 4a formed in the lead sheet 4 are interrupted at intervals of a predetermined length along the advancing direction, and the nodes 4c are formed between the slits, respectively. In the slits 4a which are adjacent to each other in the width direction, the portions which are to be formed as the nodes 4c are formed with being shifted by a half pitch of the slits 4a. Therefore, the large number of slits 4a formed in the lead sheet 4 are arranged in a zigzag pattern as shown in the plan view in the circle C2 of the one-dot chain line of FIG. 3.
The lead sheet 4 in which the large number of slits 4a have been formed in the slit forming step is stretched toward both the sides in the width direction in the subsequent step of the rotary expander. As a result, the slits 4a are expanded so as to form meshes, whereby a lattice-like grid which is to be used as a battery plate of a lead storage battery is produced.
In the conventional rotary expander, the lead sheet 4 are passed between the disk cutter rolls 1 and 2, and then between the disk cutter rolls 2 and 3, or processed two times. Therefore, the rotary expander has a problem in that, as compared with a grid which is processed by an expander of the reciprocal type, a whole grid is corroded in a larger amount and the life performance is lower. Since the lead sheet is passed two times between the three disk cutter rolls 1 to 3, shavings are produced in a large amount during the process. This causes many production disadvantages such as that a production line must be frequently cleaned. Specifically, many whisker-like lead shavings adhere to a grid which is produced by a conventional rotary expander. This is considered as one of causes of reduction of the formation efficiency in the case where a grid is used as a positive plate. Moreover, this increases the load of the disk cutters 5, so that the disk cutters are often required to be replaced with new ones because of wear at intervals of one year at the shortest.
The present inventor developed a technique in which, as shown in FIG. 5, the lead sheet 4 is processed by using only two disk cutter rolls 2 and 3 that are vertically arranged. In the technique, the lead sheet 4 which has been passed through between the upper and lower disk cutter rolls 2 and 3 is horizontally pulled out and then carried out, and hence the lead sheet 4 is in an unstable condition in a carrying-out portion. Consequently, there arise problems in that the sheet faces are undulated, and that meshes of an expanded grid often have irregular shapes.
In the disk cutters 5 of the upper and lower disk cutter rolls 2 and 3, the ridges 5a perform not only a function of cutting the lead sheet 4 to form the slits 4a, but also that of vertically protruding the wires 4b by ridge-like protrusions of the ridges 5a. When the ridges 5a are moved to the lower or upper end in accordance with the rotation of the disk cutters 5, therefore, the ridges 5a vertically penetrate the lead sheet 4 to bite between the slits 4a. When the ridges 5a are further moved in an upward or downward separating direction in accordance with the rotation of the disk cutters 5, the lead sheet 4 which is to be originally carried out in a horizontal direction is caught by the ridges 5a and tends to be moved upward or downward. For example, FIG. 6 shows the state in which the lead sheet 4 is caught by the ridges 5a of the lower disk cutters 5 and tends to be once moved downward in a carrying-out portion A in accordance with the rotation of the disk cutters 5. Moreover, the horizontal direction in which the lead sheet 4 is pulled out is in parallel to the axes of the two upper and lower disk cutter rolls 2 and 3, and elongates along the reference tangential plane which is perpendicular to the plane connecting the axes. During the carrying-out process, therefore, the lead sheet 4 is separated simultaneously from the ridges 5a of the upper and lower disk cutters 5. The direction along which the lead sheet 4 is actually moved together with the ridges 5a, or in either of the upward and downward directions is unstably changed at any time depending on the current manner of biting or catching the slits 4a by the ridges 5a. As a result, the lead sheet 4 is pulled out to the carrying-out portion A while being undulated. Furthermore, the lead sheet 4 is horizontally pulled out toward the right side of FIG. 6. Even when the ridges 5a are caught between the slits 4a, therefore, the ridges will be suddenly separated from the slits in accordance with the rotation of the disk cutters 5. As a result, each time when the ridges 5a are separated from the slits 4a, a vertical vibration occurs in the disk cutter rolls 2 and 3. This also sometimes causes the phenomena in which the lead sheet 4 is undulated, and in which meshes of an expanded grid often have irregular shapes.